Currently, electronic devices are more and more widely used. Many electronic devices, such as a digital camera, a digital video recorder, a mobile phone, a tablet computer, smart glasses and the like, are provided with display units. For example, a reality environment can be presented on the display unit by an image acquisition unit of the electric device or can be viewed through the lens of smart glasses, while contents, such as texts, pictures etc., can still be presented on the display unit. There are some cases which is not convenient for the user to view the content displayed on the display unit and the reality environment in a best mode. For example, the content displayed on the display unit and the scene of the reality environment may interfere with each other, so that objects with similar color are invisible or are uncomfortable or inconvenient for the user to view. Or, as another example, the user cannot view the contents presented on the display unit comfortably. Therefore it is desired that the user can promptly and smartly adjust the display content to achieve the best viewing experience.